1. Field of the Invention
The present invention relates to a technique for inspecting inkjet nozzles to detect a non-operating nozzle.
2. Description of the Related Art
In an ink-jet printer, ink droplets are ejected from a plurality of nozzles provided at a print head. Some of the nozzles occasionally get clogged and are rendered incapable of ejecting ink droplets because of an increase in ink viscosity, formation of gas bubbles in an ink passage, and other factors. Nozzle clogging produces images with missing dots and has an adverse effect on image quality. Nozzle inspection is therefore desired to detect a non-operating nozzle. Nozzle inspection will also be referred to herein as xe2x80x9cdot loss inspection.xe2x80x9d
Numerous methods are used to inspect the nozzles of ink-jet printers, and light-based inspection is one such method. In this method, light is emitted by a light-emitting element toward a light-receiving element, ink droplets are sequentially ejected from the nozzles of the print head in the direction of this light, and the operating state of each nozzle is determined based on whether the light is actually blocked by the ink droplets ejected from the nozzles. In this type of inspection, light is focused with a lens.
Because light is focused by a lens, the thickness of the light beam is at its minimum at a certain point on the optical path and increases in the direction away from this point. For this reason, inspecting conditions differ greatly for the inspected nozzles disposed in the vicinity of the location (beam waist) at which the light beam has minimal thickness and the inspected nozzles disposed farther away from the beam waist because of their position on the print head.
A technique featuring two parallel laser beams whose beam waists are shifted along the optical path is disclosed in JPA 10-119307 as a means of addressing these problems. According to this technique, each of the two laser beams is used in nozzle inspection, and the plurality of nozzles being examined is divided between the two beams of laser light. As a result, the nozzles are inspected under more-uniform conditions than that when a single beam of laser light is used. However, this technique still fails to adequately resolve the above-described variations in the inspecting conditions along the optical axis of laser light.
Accordingly, an object of the present invention, is to provide a technique whereby a non-operating nozzle can be detected with higher accuracy.
In order to attain at least part of the above and related objects of the present invention, there is provided a printer for printing images by ejecting ink droplets from a plurality of nozzles. The printer comprises a print head having a plurality of nozzles; and a sensor including a light-emitting element configured to emit detection light which has a substantially circular cross-section and a light-receiving element configured to receive the detection light, and configured to inspect operation of a nozzle by determining whether the detection light has been blocked by the ink droplets ejected by the nozzle. The sensor further comprises a first condensing element configured to condense the detection light, and an apertured element having a substantially circular aperture for the detection light. The aperture has a size of a same order as the cross-section of the detection light. The detection light intersects an ejecting path of the ink droplets at an exit side of the apertured element and the first condensing element.
In the printer in accordance with the present invention, a light-emitting element, a first condensing, an apertured element and a light-receiving element are provided. The light-emitting element is configured to emit detection light. The first condensing element is configured to condense the detection light. The apertured element having an aperture for the detection light. The light-receiving element is configured to receive the detection light after the detection light intersects a path of the ink droplets ejected by a nozzle. Then the detection light is emitted from the light-emitting element. Ink droplets are ejected from a nozzle. A non-operating nozzle is detected by determining whether the detection light received by the light-receiving element has been blocked by the ink droplets.
Adopting such an arrangement allows the light beam for detecting ink droplets to be constricted through the aperture. At the same time, the narrowest portion of the light beam can be expanded because of a reduction in the angle at which the light is focused. In other words, the thickness of the light beam can be made more uniform along the optical axis. It is therefore possible to reduce variations in the inspecting conditions along the optical axis of the light beam and to inspect the ejection of ink droplets with higher accuracy.
The apertured element may comprise a regular polygonal aperture having four or more angles. These apertures make the cross-section of the light substantially circular. It is more preferable that the apertured element comprises the regular polygonal aperture having six or more angles. Such aperture makes the cross-section of the light nearer circular.
The apertured element is preferably disposed at an exit side of the first condensing element. Minute ink droplets are scattered when an ink droplet is ejected in inspection. But adopting the above-described arrangement allows the scattered ink droplets to be blocked by the apertured element, and makes it less likely that the condensing element will be contaminated. The first condensing element may be disposed at an exit side of the aperture of the apertured element.
The sensor preferably further comprises an angle-adjusting element configured to adjust a direction of emission of the detection light. This allows the direction of the detection light to be adjusted for more-uniform conditions for inspecting the ejection of ink droplets by each nozzle.
The sensor preferably further comprises a position-adjusting element configured to adjust a position of the light-emitting element in a direction intersecting the direction of emission of the detection light. Such an arrangement allows the position of the light-receiving element to be adjusted such that the light-receiving element can accurately receive light when the position of the light emitting element has the deviation.
When the plurality of nozzles are disposed on a same nozzle plane of the print head, the angle-adjusting element is preferably configured to adjust the direction of emission of the detection light within a plane perpendicular to the nozzle plane. Adopting this arrangement allows the direction of emission of the detection light to be adjusted such that the optical axis remains parallel to the nozzle plane.
The angle-adjusting element preferably adjusts the direction of emission of the detection light about an axis intersecting an optical path of detection light within confines of the aperture. Adopting this arrangement allows the center position of the detection light in the aperture to remain constant when the direction of emission of the detection light is adjusted.
The sensor preferably further comprises a first ink mist screen having a first aperture for the detection light. The first ink mist screen is disposed at an exit side of the first condensing element and the apertured element, and divides a first area including the light-emitting element, the first condensing element, and the apertured element, and a second area in which the ink droplets are ejected in a direction of an optical path of the detection light.
Adopting this arrangement allows the first ink mist screen to prevent the light-emitting element or the condensing element from the deposition of the ink mist produced during the ejection of ink droplets by the nozzles. The light-emitting element and first ink mist screen are therefore less likely to suffer reduced performance, and the ejection of ink droplets can be inspected with consistent accuracy when the sensor is operated for a long time.
The printer preferably comprises a plurality of first ink mist screens. The first apertures of the first ink mist screens should be made as small as possible to reduce contamination with ink mist, but must still have sufficient radius to be able to transmit light. For this reason, the apertures cannot be made smaller than a certain size. Adopting this arrangement allows the size of the first apertures to be kept sufficiently large to transmit rectilinearly propagating light, and at the same time causes the ink mist carried by the gas flow to settle down between the first ink mist screens or to deposit on the structures between the first ink mist screens, preventing this mist from reaching the light-emitting element or first condensing element.
The sensor preferably further comprises a second condensing element disposed at an exit side of the first condensing element and the apertured element. The second condensing element having a light reception region with a prescribed surface area, and focuses the detection light received in the light reception region. The detection light intersects an ejecting path of the ink droplets at an incident side of the second condensing element.
The result is that even when light diverges from the initially intended emission direction due to a misalignment, the light beam can still be focused by the second condensing element, refracted, and directed toward the light-receiving element as long as the illumination position falls within the light reception range of the second condensing element. Consequently, there is only a slight chance that the ability of the light-receiving element to receive light will be adversely affected, and the inspecting function cannot be easily compromised even when emitted light deviates from the intended direction.
The sensor further preferably comprises a second ink mist screen having a second aperture for the detection light. The second ink mist screen is disposed at an exit side of the first condensing element and the apertured element, and divides a first area including the light-receiving element and the second condensing element, and a second area in which the ink droplets are ejected in a direction of an optical path of the detection light.
Adopting this arrangement allows the second ink mist screen to prevent ink mist from depositing on the light-receiving element or second condensing element. The light-receiving element and second ink mist screen are therefore less likely to suffer reduced performance, and the ejection of ink droplets can be inspected with consistent accuracy during an extended operation.
The printer preferably includes a plurality of second ink mist screens. As with the case in which a plurality of first ink mist screens are provided, adopting this arrangement can be effective for preventing ink mist from reaching the light-receiving element or second condensing element.
The light-emitting element is preferably mounted on a base member such that a vertical angle of the detection light can be adjusted, and the light-receiving element is preferably mounted on the base member to be able to move horizontally. The light-emitting element and the light-receiving element may share the base member and also may have it independently. The printer is preferably further comprises a first fixing element fixing the light-emitting element to the base member at an adjusted angle; and a second fixing element fixing the light-receiving element to the base member at a prescribed horizontal movement position.
In this case, the light-emitting element is preferably mounted on the base member such that the vertical angle of the detection light can be adjusted about a fulcrum shaft formed in a horizontal direction. The first fixing element preferably comprises a first tightening screw for preventing the light-emitting element from rotating about the fulcrum shaft.
According to a preferred embodiment, the light-emitting element preferably has a hyperbolic slit centered around the fulcrum shaft, and is configured such that the first tightening screw is fastened to the base member via the hyperbolic slit.
In this case, a first metal plate member is preferably further disposed between the first ztightening screw and the light-emitting element provided with the hyperbolic slit; so that tightening stress produced by the first tightening screw is transmitted to the light-emitting element via the first metal plate member; and rotation of the first tightening screw is prevented from reaching the light-emitting element.
According to a preferred means for implementing this concept, the first metal plate member preferably has a pawl, the pawl is configured to be hooked to part of the base member, and prevents the first metal plate member from rotating during the fastening of the first tightening screw.
In addition, the fulcrum shaft is formed at a position in which an axis of the fulcrum shaft intersects the aperture of the apertured element.
A slide mechanism is preferably formed between the light-receiving element and the base member, the slide mechanism has a groove formed in the horizontal direction and a protrusion configured to slide inside the groove. The light-receiving element is preferably mounted by means of the slide mechanism to be able to move horizontally in relation to the base member.
In this case, the protrusion is preferably formed at two locations set apart from each other.
According to a preferred embodiment, the light-receiving element preferably further comprises a rectilinear slit. A second tightening screw as the second fixing element is fastened to the base member by means of the rectilinear slit.
A second metal plate member is preferably further disposed between the second tightening screw and the light-receiving element having the rectilinear slit, so that tightening stress produced by the second tightening screw is transmitted to the light-receiving element via the second metal plate member; and rotation of the second tightening screw is prevented from reaching the light-receiving element.
According to a preferred means for implementing this concept, the second metal plate member preferably has a pawl. The pawl is configured to be hooked to part of the base member, and prevents the second metal plate member from rotating during the fastening of the second tightening screw.
In the printer thus configured, a sensor composed of an optical unit is disposed along the travel path of the print head, and ejecting conditions are inspected for the ink droplets ejected by the nozzles of the print head. In this sensor, the light-emitting element, which is configured to project the detection light, and the light-receiving element, which is configured to receive the detection light from the light-emitting element, are mounted on common base members. The light-emitting element is designed such that the vertical angle of the detection light projected by the light-emitting element can be adjusted. The light-receiving element is designed to allow for horizontal movement.
Consequently, the optical axis of the detection light from the light-emitting element to the light-receiving element can be readily aligned by adjusting the vertical angle on the side of the light-emitting element, and the horizontal position on the side of the light-receiving element. The optically adjusted light-emitting element can be fixed to the corresponding base member by the first fixing element. The light-receiving element can be fixed to the corresponding base member by the second fixing element.
In this case, a tightening screw is prepared as the first fixing element. The light-emitting element set to a prescribed angle in the vertical direction is fixed to the corresponding base member by the tightening screw. According to the preferred embodiment described above, the light-emitting element is provided with a hyperbolic slit centered around a fulcrum shaft formed in the horizontal direction, and the tightening screw is fastened to the base member via the hyperbolic slit. The light-emitting element can thus be readily fixed to the base member in a state in which a prescribed vertical angle is established.
A slide mechanism is formed between the light-receiving element and the corresponding base member by combining a groove formed in the horizontal direction and protrusion designed to slide inside this groove. This arrangement makes it easier to finely adjust the horizontal position of the light-receiving element in relation to the base member. In this case, the light-receiving element can be prevented from oscillating in the horizontal direction and optical adjustments can be facilitated by adopting an arrangement in which protrusion sliding inside a groove are formed at two locations set apart from each other.
Similarly, a tightening screw is prepared as the second fixing element for fixing the light-receiving element to the base member, and the light-receiving element disposed at a prescribed horizontal position is fixed to the base member by the tightening screw. According to the preferred embodiment described above, the light-receiving element is provided with a rectilinear slit, and the tightening screw is fastened to the base member through the slit. The light-receiving element can thus be readily fixed to the base member while kept at a prescribed horizontal position.
It is also possible to adopt an embodiment in which a first metal plate member is interposed between the light-emitting element and the tightening screw serving as the first fixing element, a second metal plate member is interposed between the light-receiving element and the tightening screw serving as the second fixing element, and the two metal plate members are provided with pawls for hooking with part of the base member and preventing rotation from occurring during the fastening of the tightening screws. According to this embodiment, the light-emitting element and light-receiving element can be prevented from shifting and can be securely fixed to the corresponding base members when the light-emitting element and light-receiving element are optically adjusted and fixed by the tightening screws.
The present invention can be worked as the following embodiments.
(1) Printer or print controller
(2) Printing method or print control method
(3) Computer program for operating the aforementioned device or method
(4) Storage medium for storing the computer program for operating the aforementioned device or method
(5) Data signals implemented as part of a carrier wave and designed to contain a computer program for operating the aforementioned device or method
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.